The proposed project is intended to spear-head a comprehensive research program to develop new practical strategies for analyzing the gene functions of RNA viruses by genetic manipulation of the cloned genes. In this project, we aimed at converting the entire spectrum of the gene expression products of measles virus from mRNAs into functional and expressible cDNA clones. By gene transfer, specific genes of the measles virus will be expressed in environments amenable to detail biochemical and functional analyses. The effects of over-expression and under-expression of specific viral genes on the replication of measles virus will be critically examined to gain insight into the biological roles of the viral genes. The materials and knowledge thus obtained will be used to fully define the putative detect(s) in the genomes of several strains of subacute sclerosing panencephalitis (SSPE) viruses. Specific SSPE viral genes will be cloned and the putative defect(s) will be characterized at the structural and functional levels. Novel approaches will be developed to generate specific recombinant RNA viruses via cloned gene-mediated complementation ad rescue experiments.